When Bill Tilman travelled to the Pakistan Karakoram in 1937, he hoped to solve two unexplained geographical riddles: the existence of an icecap in Central Asia, and a glacier without any river outlet. He relished the opportunity to prove the scientists wrong.

The great Tyrolean mountaineer Reinhold Messner famously claimed to have seen a yeti when he was camping alone in a clearing in Tibet in 1986. Whatever it was, it moved adeptly on two legs and was too big to be